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- M. Stetter, E. W. Lang, and
K. Obermayer. Unspecific long-term potentiation can evoke functional
segregation in a model of area 17.
.
NeuroReport, 9:2697-2702, 1998.
(FTP Gzipped PostScript, 15 pages, 397 kb)
Recently it has been shown in rat hippocampus that the synapse
specificity of Hebbian long-term potentiation breaks down at short distances
below 100 mum. Using a neural network model we show that this unspecific
component of long term potentiation can be responsible for the robust
formation and maintainance of cortical organization during activity driven
development. When the model is applied to the formation of orientation and
ocular dominance in visual cortex, we find that the addition of an unspecific
component to standard Hebbian learning - in combination with a tendency of
left-eye and right-eye driven synapses to initially group together on the
postsynaptic neuron - induces the simultaneous emergence and stabilization of
ocular dominance and of segregated, oriented ON-/OFF-subfields. Since
standard Hebbian learning cannot account for the simultaneous stabilization
of both structures, unspecific LTP thus induces a qualitatively new
behaviour. Since unspecific LTP only acts between synapses which are locally
clustered in space, our results imply that details of the local grouping of
synapses on the dendritic arbors of postsynaptic cells can considerably
influence the formation of the cortical functional organization at the
systems level. Key Words: visual cortex, developmental model,
correlation-based learning, unspecific LTP, self-organization, neural
network
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